The goal of the proposed training plan is to further develop the applicant's knowledge and research skills in the areas of substance use and neuropsychology and to integrate this with an understanding of ecological momentary assessment (EMA) and data analysis. The ultimate goal of the proposal is to conduct a dissertation project that will deepen the applicant's knowledge of research design and analytic issues addressing the topic of cognitive and affective situational factors surrounding cannabis and tobacco use and the field's knowledge of the momentary factors that contribute to conjoint cannabis and tobacco use among young adults. Given the skills that will be developed and the knowledge that will be gained, this project is a necessary step in achieving the applicant's career goal to pursue a faculty position in an academic setting where independent investigations can be conducted. The training plan proposed includes structured course work, regular sponsor meetings, experience with EMA data collection and analysis, and professional development activities. The proposed research furthers this training plan by examining the conjoint effects of simultaneous cannabis and tobacco use on neurocognitive, affective and behavioral outcomes in young adult tobacco users. The motivation for examining this particular drug combination comes from the increasing number of young people reporting combined use of cannabis and tobacco, the health consequences associated with conjoint use (e.g., greater dependence symptoms, fewer successful quit attempts), and the limited number of investigations examining the mechanisms that maintain simultaneous use. Given that young adults are highly influenced by contextual variables, EMA techniques are an optimal method for assessing the potential neurocognitive and affective factors that reinforce conjoint use. The specific aims of this study are: 1) to examine the effects of simultaneous use of cannabis and tobacco on momentary levels of neurocognitive functioning, namely changes in working memory and to compare these effects to the effects of cannabis and tobacco alone; 2) to examine the effects of simultaneous use on momentary changes in affect and subjective cannabis intoxication and to compare these effects to the effects of cannabis and tobacco alone; and 3) to examine the link between momentary changes in neurocognition, affect and subjective intoxication on behavioral outcomes (e.g., dependence and problematic use). Data will be collected from 325 young adults currently enrolled in a large, ongoing longitudinal investigation of the social and emotional contexts of young adult tobacco use. Mentorship for this project will be provided by experts in the areas of tobacco use and EMA methodology (Dr. Robin Mermelstein), cannabis use and the neuropsychology of addiction (Dr. Raul Gonzalez), and hierarchical longitudinal data analysis (Dr. Robin Mermelstein and Dr. Donald Hedeker). This area of research is in its nascent stages, and this study will be one of the first to examine conjoint effects of cannabis and tobacco as well as to integrate neurocognitive and EMA measures to the study of this understudied phenomenon. Not only will the proposed plan be instrumental in propelling the applicant's career forward, but also promises to yield results that will be directly applicable to the development of prevention and cessation efforts for young adult tobacco users who also use cannabis.